The present invention is generally directed to active matrix organic light-emitting diode (AMOLED) displays which are enhanced by passivating the entire active array surface with an insulating layer, thereby substantially reducing or eliminating electrical shorts across the organic light-emitting diode (OLED) layer from the top electrode to the bottom electrode.
AMOLED displays differ from active matrix liquid crystal diode (AMLCD) displays in a number of important ways, the most fundamental being that AMOLEDs are emissive type displays where the light emitted is generated by recombination of electrons and holes in a thin zone of the OLED material itself, whereas LCDs have a bright backlight as the light source, and each pixel is essentially a light valve, where grayscale is achieved by controlling the polarization state of the liquid crystal (LC) material relative to fixed polarizers attached in front of, and behind the LC sandwiched layer. This affords an AMOLED a number of advantages: there is no need for polarizers, backlight, color filter alignment (in the case of RGB OLED materials) or glue seal, and LC fill steps. As such, AMOLEDs can be made thin, and bright, with no viewing angle dependence or color shift problems associated with the electro-optical properties of AMLCDs.
Despite the myriad of advantages and the promise of tremendous commercial impact in the world of display technology, there remains a number of technical problems to solve before the full potential of AMOLED technology can be fully realized. One of these problems which is addressed by the present invention, arises because the entire OLED stack is usually quite thin (on the order of 100 nm) compared to the typical cell spacing in an AMLCD (about 5 um). This poses problems at the edges of the patterned electrodes, which themselves are typically 30 to 100 nm thick, depending on whether or not they are transparent or reflective. Transparent conductors such as ITO are typically wet-etched, and often have near vertical sidewalls which are very difficult to cover, especially when using small molecule OLED materials which are thermally evaporated, and thus have line-of-sight coating issues. In addition, many metals grow in a columnar fashion and also give near vertical sidewalls when wet-etched.
The present inventors have unexpectantly discovered that the aforementioned problems may be solved by passivating the entire active array surface with a final insulating layer, which, among other things, may include PECVD deposited SiOx, or SiNx, a spin-on insulating polymer film, etc. If such a layer is deposited, patterned and etched in such a way that the lower patterned electrode sidewall is completely coated, while a shallow taper angle is achieved at the point where the passivation layer meets the electrode surface, the possibility of electrical shorts across the OLED layer from the top electrode to the bottom is substantially eliminated or dramatically reduced. Therefore, one aim of the present invention is to electrically passivate the bottom electrode from the top electrode to prevent unintended shorting. Among other characteristics, this entails having an acceptable quality insulator.
Another aim of the present invention is to increase the chemical robustness during fabrication processing and after fabrication processing. Among other characteristics, this entails having an acceptable layer the provides: (1) acceptable selective etch ratio between the layer and the bottom electrode and underlying layers, (2) acceptable etch stop layer between the layer and subsequent layer processing, and (3) acceptable chemical barrier without being a source of element diffusion or degradation to the other film""s properties.
Still another aim of the present invention is to increase, or at least not change, the optical efficiency of the subsequent OLED structure. Among other characteristics, this entails having an acceptable layer that provides either optical absorption or optical transparency.
The present invention also provides many additional advantages which shall become apparent as described below.
An active or passive matrix organic light-emitting diode comprising an organic light-emitting diode portion, the organic light-emitting diode portion comprising: an underlayer having a top surface and bottom surface; a first electrode layer which is deposited and patterned on the top surface of the underlayer such that at least a portion of the underlayer is exposed, wherein the deposited first electrode layer comprises a top surface, a bottom surface and sidewalls disposed between the top and bottom surfaces, the sidewalls are positioned adjacent to the exposed portion of the underlayer; a passivation layer deposited on the exposed portion of the underlayer and the peripheral regions of the first electrode layer such that the passivation layer covers the sidewalls and the peripheral regions of the first electrode layer; a transparent conductor layer deposited on the passivation layer and the non-peripheral regions of the first electrode layer; and a second electrode layer deposited on the transparent conductor layer.
Preferable, the first electrode layer is a pixel anode, the second electrode layer is a cathode, the transparent conductor layer is an organic light-emitting diode, and the passivation layer is at least one selected from the group consisting of: SiOx, SiNx, an insulating polymer material, or a combination thereof.
The passivation layer is preferably tapered toward the first electrode layer, such that a shallow taper angle is achieved at the point where the passivation layer meets the top surface of the first electrode.
The present invention also includes a method for forming an active matrix organic light-emitting diode comprising: (a) depositing and patterning a first electrode layer on the top surface of an underlayer such that at least a portion of the underlayer is exposed, wherein the deposited first electrode layer comprises a top surface, a bottom surface and sidewalls disposed between the top and bottom surfaces, the sidewalls are positioned adjacent to the exposed portion of the underlayer; (b) depositing a passivation layer on the exposed portion of the underlayer and the peripheral regions of the first electrode layer such that the passivation layer covers the sidewalls and the peripheral regions of the first electrode layer; (c) depositing a transparent conductor layer on the passivation layer and the non-peripheral regions of the first electrode layer; and (d) depositing a second electrode layer on the transparent conductor layer.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings, wherein like parts have been given like numbers.